I have a choice of 4 ratchets and a ratchet spanner and it was still easier to drop the manifold than dick around with the bottom 3 rocker cover bolts. Made for a very tidy re-installation too. You heard it here first!

How much fluid is required to do it with the above method from experience?

Fluid is just below min level and don't know when it was last changed so thought might as well give it a flush (thanks to JWS service invoices being a very detailed "Service on GD Impreza WRX").

They wouldn't have replaced it as part of a service, it isn't scheduled. I would use about 2-3 litres for a flush/replacement. Subaru P/S systems use dexron 3 ATF as a fluid.

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F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i

^^ What he said.. 2-3 litres, and to do it properly you do want to remove the return line, start the car and pour new fluid in while the old fluid is been pumped out of the return, once it comes out clean from the return she's all good. I only used 1.5L but it depends on how dirty the system is.

Easier if you have two people doing it, one person pouring in the fluid and the other turning on/off the vehicle!